This invention relates to a process of cleaning waste gases generated in an at least partially covered movable grate-type sintering line, said sintering line comprising an ignition zone, a sintering zone and a burning zone.
Waste gases generated in sintering installations are known to contain pollutants other than dust. In for example, iron ore sintering plants, compounds of lead, tin, zinc, arsenic, cadium, copper, sulfur, chlorine, fluorine, nitrogen oxides and the like as well as hydrocarbons are generated. These pollutants originate both from the ore mixture itself and from the solid, liquid or gaseous fuels used to sustain the sintering process.
It appears likely that future environmental regulations governing the discharge of solid and gaseous pollutants into the atmosphere will become more and more strict and lower and lower allowable limits on such discharges will be set.
Present clean air regulations in, for example, Germany prescribe that dust levels in waste gases not exceed a value of less than 150 mg/Nm.sup.3 . For other pollutants, such as, for example, gaseous emissions of SO.sub.2, fluorine, nitrous oxide and other components of the waste gas, limiting values which are dependent upon local conditions are established. The VDI-Guideline 2095 (page 9) sets, for example, minimum flue heights as a function of the SO.sub.2 emission in kg/h as an economically feasible solution. However, the problem of the elimination of said pollutants is not solved by great flue heights. They are only distributed over a greater space and thereby are reduced in their local concentration.
In a conventional sintering process having a single suction system over the entire sintering line, a very large quantity of waste gas having an average temperature of approximately 120 .degree. C. to 180 .degree. C. is ejected into the atmosphere by dust collectors.
The composition of the waste gases, as well as the dust, is variable in the longitudinal direction of the sintering line from the ignition to the discharge, and different pollutants tend to form in specific sections of the suction apparatuses in the normal operation of the sintering plant.
With the present requirements for dust removal, electrostatic precipitors are used for fine-grained dust and mechanical dust collectors are used for coarse-grained dust. If, for example, the removal of SO.sub.2 is also necessary for the entire waste gas of such sintering installations after the dust removal, the operating and investment costs become relatively high.